For example, a pressurized water reactor (PWR) or a boiling water reactor (BWR) uses light water as a nuclear reactor coolant and a neutron moderator. In a normal operation mode of the nuclear reactor, the nuclear reactor coolant cools a cladding pipe of nuclear reactor fuel so as to decrease the temperature of the cladding pipe.
In order to check the integrity of the nuclear reactor fuel when operating the nuclear reactor in the normal mode, a nuclear reactor coolant and a gas dissolved in the nuclear reactor coolant are periodically sampled from the nuclear reactor. Then, a concentration of a specific radionuclide which may be discharged from the nuclear reactor fuel to the nuclear reactor coolant and the dissolved gas is monitored.
For example, Patent Literature 1 discloses a radioactive gas measuring device which extracts the gas dissolved in the nuclear reactor coolant, seals the gas in a sample chamber, and monitors a radiation level of a radioactive gas.